The present invention relates to an image forming apparatus.
Many image forming apparatuses such as electronic copying machines have a manual paper feeder in addition to an automatic cassette paper feeder. Commonly, this manual paper feeder is used to temporarily feed to the main body a paper sheet of a type outside the specification of an automatic paper feed tray. The basic position of such a manual paper feeder remains unchanged at present.
Recently, however, demands on manual paper feeders are more and more increasing. That is, manual paper feeders are required not only to correspond to various types of paper sheets (particularly basis weights) but also to continuously feed a plurality of paper sheets like automatic paper feeders.
These requirements have been conventionally met by adjusting the position, material, shape, and pressing force of each of a paper pickup roller for picking up a paper sheet, a paper feed roller for feeding the picked-up sheet to the main body, and a brake pad for stopping the sheet, as the basic components of a manual paper feeder, or by adjusting the position, angle, guide angle, and the like of a paper stack tray.
Unfortunately, the adjustment of these components such as the paper pickup roller, paper feed roller, brake pad, and paper stack tray cannot unlimitedly cope with diverse types of paper sheets.
Major problems are as follows.
(1) To reliably separate and feed paper sheets having a high friction coefficient between them, a pre-separation function such as an inclined separation guide must be placed before a separation mechanism. However, when the paper feed properties of thick paper sheets are taken into consideration, the guide shape of a paper conveyor for conveying paper sheets must be infinitely approached to a straight line. This contradiction makes it difficult to obtain an appropriate angle meeting the two requirements.
(2) When a condition such as a thickness changes, the friction coefficient and the paper feed property change. Hence, it is difficult to accurately separate and feed such a plurality of types of paper sheets.
In some conventional apparatuses, a manual paper feeder has a tray with an elevating function which can move up and down in accordance with the number or basis weight of paper sheets, like an automatic cassette paper feeder. This system can always maintain the posture of a paper sheet in a stable state regardless of changes in the number or basis weight of paper sheets.
The mechanism, however, of this manual paper feeder becomes complicated and increases in size like an automatic paper feeder. This is a disadvantage in seeking the space utility of an apparatus as a whole.
The present invention has been made in consideration of the above situation, and has as its object to provide an image forming apparatus capable of reliably separating and feeding different types of paper sheets to the main body, with a simple mechanism which can be made small.